When I went through this certification path a couple years ago I did in this order: GCP > Outbound Dialer > Architect > Developer. I work with other engineers on our team who did them in different sequence (always left the Developer to the last though). GCP should probably be the first one to give someone a good base knowledge. There is no requirement for taking any exam, so as long as you are familiar with the material.
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Michael Jewell
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